The invention relates to an apparatus and method of cracking connecting rods used in internal combustion engines in which the rods are supported on a fixture mounted on a conveyor that transports the rods through a plurality of stations where each rod is split into a body and cap, the crack zone is cleaned, and the body and cap are reunited and bolted together before being removed from the fixture.
The connecting rod in an internal combustion engine couples the crankshaft to a piston. The small end of the connecting rod has a small bore that is coupled to the wrist pin on a piston and big end of the connecting rod has a big bore that is coupled to the eccentric pin on a crankshaft. Because of the physical construction of the crankshaft, the big end of the connecting rod has to be separated into two pieces in order to be mounted on the pin. In the past, the normal practice was to initially mold and machine the connecting rod in two pieces that would then bolted together on the crankshaft pin.
As engine manufacturers required greater precision, it was found that molding and machining the connecting rod in two pieces and then assembling the pieces together would not give as perfect a fit on the crankpin as could be achieved if the rod was initially cast in one piece and then split or cracked at the centerline of the big bore. The two pieces will fit perfectly together because the irregularities of the split match up to one another when the two pieces are reassembled.
According to the invention, the big end of a connecting rod is mounted on a split mandrel that is carried by a fixture. The fixture is transported through several operations by means of a conveyance system, and the conveyance system transports a plurality of similarly equipped fixtures. The big end of the connecting rod is split or cracked using two opposing wedges that are driven into a passageway formed between the mandrel halves. The two opposing wedges create equal and opposite horizontal forces and accumulative vertical forces. The horizontal forces cancel each other out, and the vertical forces separate the split mandrel along a line that is parallel to the plane of the connecting rod and perpendicular to the axis of the bore in the big end. A low pressure is first used to push the two wedges toward each other to take out any clearance between the components. A high pressure is then applied to the wedges to rapidly separate the connecting rod cap from the connecting rod body. Means are provided to limit the separation between the connecting rod cap and body after one side of the rod has cracked in order to limit the distortion of the uncracked side before it also cracks. Once both sides of the rod have cracked and the connecting rod cap is separated from the body, the gap between the cap and the body is increased and held open until the crack zone can be cleaned. After cleaning, the connecting rod cap and body are bolted together and are then removed from the fixture.
It is accordingly an object of the invention to provide a connecting rod cracking apparatus in which the connecting rod is mounted on a fixture that circulates through several operations by means of a conveyance system.
It is another object of the invention to provide a connecting rod cracking apparatus in which the connecting rod is cracked by a single force acting in a single direction by using two opposing wedges that are driven into a passageway formed between the halves of a split mandrel.
It is another object of the invention to provide a connecting rod cracking apparatus in which means are provided to limit the separation between the connecting rod cap and body after one side of the rod has cracked in order to limit bending distortion of the uncracked side.
It is another object of the invention to provide a connecting rod cracking apparatus in which means are provided to separate the cap from the body after the cracking has occurred so that crack debris can be removed from the crack zone before the cap and the body are reunited.
It is another object of the invention to provide a connecting rod cracking apparatus in which the means to crack the cap from the body travels with the fixture so that only external forces are needed at the cracking station to cause the rod to crack.
These and other objects of the invention will become apparent from the following detailed description in which reference numerals used throughout the description correspond to numerals found on the drawing figures.